1. Field of the Invention
The present invention relates to a functional device such as batteries, capacitors, sensors, photoelectric conversion devices, photoelectrochemical cells, recording devices, electrochromic devices. Precisely, the invention relates to a functional device in which the flat band potential (Vfb) of the semiconductor is controlled as containing a specific compound.
In particular, regarding the electrochromic device for it, the invention relates to an optical device that comprises an electromotive force-generating element capable of generating an electromotive force in accordance with the intensity of electromagnetic waves, and an electrochromic device, and relates to an image-taking unit that comprises the optical device.
2. Description of the Related Art
In a functional device such as batteries, capacitors, sensors, photoelectric conversion devices, photoelectrochemical cells, recording devices, electrochromic devices, the reaction with the functional material that may occur in the semiconductor surface may often have some significant influences on the quality of the devices. Typical examples of a color-sensitized photoelectric conversion device are in U.S. Pat. No. 4,927,721 and JP-A 1-220380; and typical examples of an electrochromic device are in U.S. Pat. Nos. 6,067,184, 6,426,827, 6,605,239, 673,405, and JP-T 2003-511837. For the reaction on a semiconductor surface, the flat band potential of the semiconductor material is important. This is because, when a semiconductor material and a functional material undergo electron transfer on a semiconductor surface, then the electron shall pass through the valence band end (that is, the flat band potential) of the semiconductor material.
It is known that the flat band potential of a semiconductor material is intrinsic to the semiconductor material and it may change depending on pH (for example, Hiroshi Tubomura, Photoelectrochemistry and Energy Conversion, published by Tokyo Kagaku Dojin, and S. Roy Morrison, Electrochemistry at Semiconductor and Oxidized Metal Electrodes, published by Plenum Press). However, the method of flat band potential control is not always satisfactory.
The flat band potential may be controlled by selecting a semiconductor material, but even though the flat band potential of the selected material is on a suitable level and the improvement in the quality of functional devices could be expected from it, the semiconductor material would be of no use if it is expensive or is a dangerous substance. On the contrary, even though a semiconductor material could be produced relatively inexpensively and is safe and stable, its expression effect in functional devices may be small if its flat band potential is not on a suitable level. A method is desired capable of controlling the flat band potential of a semiconductor material independently of the semiconductor material itself.
The potential control may be possible by pH control. However, an organic solvent is often used in functional devices because of the functional limitation thereon, and a control method except pH is desired.
In a color-sensitized photoelectric conversion device, when a pyridine compound-containing electrolyte is used as in JP-A 2004-47229, JP-A 2004-171821 and JP-A 2004-273272, then it is reported that the inverse current is prevented and the open-circuit voltage rises. However, the prevention of inverse current is not always satisfactory, and a better method of inverse current prevention is desired. As will be obvious from the examples of a color-sensitized photoelectric conversion device, desired in the art are an all-purpose semiconductor flat band potential control method and a semiconductor flat band potential-controlled device of general applicability to all functional materials including semiconductor materials.